It is known to capture non-flash images followed by flash images and by subtracting these images (including some luminance normalizing), one can get a difference image which indicates where red-eye defects (flash-eyes) are located. U.S. Pat. No. 7,027,662 and U.S. Pat. No. 6,859,565 are incorporated by reference.
In addition, US published patent application 2005/0041121, entitled “Red-eye filter method and apparatus”, which is assigned to the same assignee as the present application and incorporated by reference, describes techniques wherein a reference non-flash and the main flash image may initially be of different sizes, and where the images are sized to the same dimensions and aligned before luminance normalization and/or subtraction.
It is desired to have an improved technique involving capturing two images that are normalized for luminance and then subtracted, indicating the likely eye locations in a main acquired image, followed by acquisition of a main image. The process would be performed quickly (typically less than 1 second) to minimize any misalignment of the reference pair and the main acquired image.
It is also desired to have a technique that overcomes problems associated with the non-flash image tending to be significantly darker than the flash image and, particularly in indoor environments, wherein it is difficult to achieve practical luminance normalization.